Rheostat



Feb 24, 1931. BENNETT 1,793580 RHEOSTAT Fi ld Jan. 14, 1927 E- 1 M MM 5 Patented Feb. 24, 1931 UNITED STATES PATENT OFFICE MORRIS H. BENNETT, OF WATERBURY, CONNECTICUT, ASSIGNOR;TO SCOVILL MANU- FACTURING COMPANY, OF WATERBURY, CONNECTICUT, A CORPORATION OF CON- RHEOSTA'I j Application filed January 14, 1927.. Serial No. 161,045.

This invention relates to improvements in variable rheostats such as are generally employed in radio receiving apparatus.

It is desirable in this class of rheostat,

which are to control and regulate small currents, that the resistance 0011 be somounted that it will be prevented from shifting its position, and it is the especial obpectof this invention to provide improved means for securing the coil in such manner that it will be maintained in proper position and prevented from shifting. Many attempts have heretofore been made to accomplish th s result but they have not been found satisfactoryv in practice.

i A further object of the invention is to produce a rheostat which will be simple in number of parts, cheap in cost of manufacture and easy to assemble.

With the above objects in view and some others which will be obvious to thoseskilled in the art from the description hereinafter, the invention consists in the features, details of construction and combination of parts which will first be described in connect1on with the accompanying drawings and then more particularly pointed out.

In the drawin s:

Figure 1 is a ront elevation of a rheostat embodying the features of the present invention' Figure 2 is a cross-section on the line 2-2 of Fi re 1' Fig liie 3 is a sectional view of the rheostat mounted on the front panel of a radio receiving instrument;

Figure 4: is a detail v ew of the clamp; and

Figure 5 is a view similar to Figure 2 before being drawn into position. I

Referring to said drawings:

A coil of any suitable resistance wire A is arranged in. close symmetrical loopssnugly about a core B of any suitable insulating material, as fibre. The resistance wire may advantageously be arranged in the form of a helix and bent into substantially the form of a circle and it will also be of advantage to have the fibre core of such thickness and material that it will easily bend in the form of a circle to conform with its surrounding resistance wire. These loops of wire are arranged close together about the core in order that the difference in resistance between succeeding coils of the wire will be slight, thus permitting very close control of the variation in current. The resistance coil Wlll not form a complete circle but space will be afforded between its ends to allow a clamp to be applied for securing together the ends of the fibre core.

A bracket M of any'suitableconducting material, as brass, is arranged to act as a support for the fibre core and resistance coil. It will befound advantageous to strike this bracket up from a single piece of metal to form two armsa and b, the former of which lies horizontally withinthe coil and core and has its inner end 0 extending slightly beyond the center of the circle formed by the core and resistance. Arm a is provided with an opening near its inner end 0, which opening is concentric with the circle. This opening is of such size that it allows threaded portion d of hub or barrel II to be snugly fitted therein, this barrel having a body portion provided with a shoulder e whichrests against and is supported on the upper side of said bracket arm (1. Hub H will be retained in position with its shoulder against the arm a by nut 0.

Hub H may be variously constructed and of any suitable material, that herein illus trated being in one piece, of brass, and having at its upper end a cylindrical portion 9 ex-c tending about half its length, next to which is a screw threaded portion (Z of slightly less diameter than said cylindrical portion, thus forming a shoulder e and this screw threaded portlon in turn terminates in a cylindrical portion is of about the diameter of the body of the screw threaded portion. Hub H is perforated centrally throughout its length to allow spindle Z to pass therethrough.

It will' be advantageous to so arrange bracket arm I) that it will lie at slightly acute angle to the arm a. By arranging the arms a and b of bracket M at a slightly acute angle the pressure on bracket arm a, caused by tightening nut 0, produces such a pull on arm 7) that it causes a kind of lever action on the resistance coil and core by drawing bracket arm 6 and with it the resistance wire and core secured thereto toward the front panel C lever action the fulcrum is about at the juncit to actas a-stop and thus prevent finger F making a complete circuit of said resistance wire.

Arm may be secured in any suitable H1311: ner to a supporting plate P, which plate, as shown, is of substantially rectangular shape, its width being slightly greater than that of "the core B and having its top, andjbfo'ttomjendfs turned inward substantially at rightan'gles, totake over the top and bottom of said core B. In the present example, plate P is provided with two holes about equidistant from its ends to register with twosimilar holes in bracket arm I). w, L

At one of the ends of plate P, which plate may be of any suitable conducting material, as brass, will be arranged a terminal. 9' for securing thereto'one of the lead wires, which terminal it will be advantageous to have made an integral part of plate P, as shown. A-"sec- 0nd lead wire terminal f of any suitable conducting material, ascopper, is attachedto one endof the resistance wire in any suitable manner, as by inserting its end under some of the terminal "coils of the rheosta't, which with the bracket arm areclose togetherbutdo, not contact, and then soldering it. a v

The ends of insulatingcore B, to Which the resistance wire has been secured in any suitable manner, as by being tightly pressed against said insulating core, "are brought closely together, but-not so they will overlap, b 011 the inner side and plate P on the outer side and held -trom.inovement in any suitablei manner, as by twoor more rivets, which may be advantageously entered from the inside, that is, such rivets will first pass through bracket arms 5, then throughtheends ofthe insulating core and then through pflate P, when the outer, or upsetting ends ofsaid frivefts will be clenched s'aidfplate P, thus seagainst the outside of curely ;l;1old'i'ng these parts together.

The trout panel Got an instrument hoard, which may be ofany suitable construction or material, as, for example, phenol condensation productyh as a hole D formed IIl'l'fi of such size and'shapethat it will-act as a bearing for rheostat operating spindle Z," hereinafter de- A. sliding contact finger F, whichmay be of anysuitable current-carrying material as,

for example, copper, is also provided. Although th s slidingcontact may be variously constructed, it will beadvantageous to haveits inner endsubstantial-ly circular to conform to the shape of'the'cylindrical end of hub H on vided with a central bore cular shaped end resting on rub H to a substantially narrow. portion near its outer end when it abruptly widens to a square end por tion Ger about its original breadth, this widened square portion being bent in the arc of a circle to furnish a rounded surface for contact on and between the loops of the resist ance coil, as shown in Fig. 1. Suchconstruc- 'tion providesa strong and resilient contact surfacecap'abl e'of easyyet certain action.

- It will be of advantagefalso, to arrange hub H so as tobe slightly less in length't-han the width of the resistance coil A. I the particular embodiment illustrated herein the hub H has a length substantially equal to that of the combined width ofresisjtance coil A and the thickness of the bracket It will be advantageous also to have hub H located centrally of the resistance coil in order thatthe contact finger may make good contact with all the loopsof the resistance coil and also that it be of proper length to allow the sliding Contact finger F to bear oneach convolution of the resistance coil in such manner that it may readily take the currenttherefrom.

Any usual dial control knobE may be used 't-o'operate the rh 'eostat. Such knob is prof to register with perforation -D= in front panel C to allow spindle Z to pass throu gh pertoration' D and into bore f, where its end ,3" will be secured by a screw to cause said end of spindle Z to move with said'knob, which will in turn cause finger F secured to the opposite end of said spindle to be moved. It will be advantaa sheet metal ele'inent'having arms arrangedat an oblique angle to each other,roneof; said arms being supported {against thepaneland the other arm supporting the rheostat whereby the rheostat is wedged against the panel by the lever action of said element" =2. The combination with apanel and a rheosta-te o f the type including a circular core member, a wire resistance-wound on thecore member, an operating spindle arranged concentrica'lly of said .core and "provided with; a

nger for engaging the wire,"of-a sheet metal element having arms arranged atlan'acute'i; J

my hand.

MORRIS H. BENNETT. 

